<?php
/**
 * Zend Framework
 *
 * LICENSE
 *
 * This source file is subject to the new BSD license that is bundled
 * with this package in the file LICENSE.txt.
 * It is also available through the world-wide-web at this URL:
 * http://framework.zend.com/license/new-bsd
 * If you did not receive a copy of the license and are unable to
 * obtain it through the world-wide-web, please send an email
 * to license@zend.com so we can send you a copy immediately.
 *
 * @category   Zend
 * @package    Zend_Pdf
 * @subpackage FileParser
 * @copyright  Copyright (c) 2005-2009 Zend Technologies USA Inc. (http://www.zend.com)
 * @license    http://framework.zend.com/license/new-bsd     New BSD License
 * @version    $Id: FileParserDataSource.php 16541 2009-07-07 06:59:03Z bkarwin $
 */

/**
 * Abstract helper class for {@link Zend_Pdf_FileParser} that provides the
 * data source for parsing.
 *
 * Concrete subclasses allow for parsing of in-memory, filesystem, and other
 * sources through a common API. These subclasses also take care of error
 * handling and other mundane tasks.
 *
 * Subclasses must implement at minimum {@link __construct()},
 * {@link __destruct()}, {@link readBytes()}, and {@link readAllBytes()}.
 * Subclasses should also override {@link moveToOffset()} and
 * {@link __toString()} as appropriate.
 *
 * @package    Zend_Pdf
 * @subpackage FileParser
 * @copyright  Copyright (c) 2005-2009 Zend Technologies USA Inc. (http://www.zend.com)
 * @license    http://framework.zend.com/license/new-bsd     New BSD License
 */
abstract class Zend_Pdf_FileParserDataSource
{
	/**** Instance Variables ****/


	/**
	 * Total size in bytes of the data source.
	 * @var integer
	 */
	protected $_size = 0;

	/**
	 * Byte offset of the current read position within the data source.
	 * @var integer
	 */
	protected $_offset = 0;



	/**** Public Interface ****/


	/* Abstract Methods */

	/**
	 * Object constructor. Opens the data source for parsing.
	 *
	 * Must set $this->_size to the total size in bytes of the data source.
	 *
	 * Upon return the data source can be interrogated using the primitive
	 * methods described here.
	 *
	 * If the data source cannot be opened for any reason (such as insufficient
	 * permissions, missing file, etc.), will throw an appropriate exception.
	 *
	 * @throws Zend_Pdf_Exception
	 */
	abstract public function __construct();

	/**
	 * Object destructor. Closes the data source.
	 *
	 * May also perform cleanup tasks such as deleting temporary files.
	 */
	abstract public function __destruct();

	/**
	 * Returns the specified number of raw bytes from the data source at the
	 * byte offset of the current read position.
	 *
	 * Must advance the read position by the number of bytes read by updating
	 * $this->_offset.
	 *
	 * Throws an exception if there is insufficient data to completely fulfill
	 * the request or if an error occurs.
	 *
	 * @param integer $byteCount Number of bytes to read.
	 * @return string
	 * @throws Zend_Pdf_Exception
	 */
	abstract public function readBytes($byteCount);

	/**
	 * Returns the entire contents of the data source as a string.
	 *
	 * This method may be called at any time and so must preserve the byte
	 * offset of the read position, both through $this->_offset and whatever
	 * other additional pointers (such as the seek position of a file pointer)
	 * that might be used.
	 *
	 * @return string
	 */
	abstract public function readAllBytes();


	/* Object Magic Methods */

	/**
	 * Returns a description of the object for debugging purposes.
	 *
	 * Subclasses should override this method to provide a more specific
	 * description of the actual object being represented.
	 *
	 * @return string
	 */
	public function __toString()
	{
		return get_class($this);
	}


	/* Accessors */

	/**
	 * Returns the byte offset of the current read position within the data
	 * source.
	 *
	 * @return integer
	 */
	public function getOffset()
	{
		return $this->_offset;
	}

	/**
	 * Returns the total size in bytes of the data source.
	 *
	 * @return integer
	 */
	public function getSize()
	{
		return $this->_size;
	}


	/* Primitive Methods */

	/**
	 * Moves the current read position to the specified byte offset.
	 *
	 * Throws an exception you attempt to move before the beginning or beyond
	 * the end of the data source.
	 *
	 * If a subclass needs to perform additional tasks (such as performing a
	 * fseek() on a filesystem source), it should do so after calling this
	 * parent method.
	 *
	 * @param integer $offset Destination byte offset.
	 * @throws Zend_Pdf_Exception
	 */
	public function moveToOffset($offset)
	{
		if ($this->_offset == $offset) {
			return;    // Not moving; do nothing.
		}
		if ($offset < 0) {
			require_once 'Zend/Pdf/Exception.php';
			throw new Zend_Pdf_Exception('Attempt to move before start of data source',
			Zend_Pdf_Exception::MOVE_BEFORE_START_OF_FILE);
		}
		if ($offset >= $this->_size) {    // Offsets are zero-based.
			require_once 'Zend/Pdf/Exception.php';
			throw new Zend_Pdf_Exception('Attempt to move beyond end of data source',
			Zend_Pdf_Exception::MOVE_BEYOND_END_OF_FILE);
		}
		$this->_offset = $offset;
	}

	/**
	 * Shifts the current read position within the data source by the specified
	 * number of bytes.
	 *
	 * You may move forward (positive numbers) or backward (negative numbers).
	 * Throws an exception you attempt to move before the beginning or beyond
	 * the end of the data source.
	 *
	 * @param integer $byteCount Number of bytes to skip.
	 * @throws Zend_Pdf_Exception
	 */
	public function skipBytes($byteCount)
	{
		$this->moveToOffset($this->_offset + $byteCount);
	}
}
